1. Field of the Invention PA1 2. Description of the Prior Art
This invention relates, generally, to a filter wherein a tank casing is divided by a tube sheet into lower and upper chambers that have respectively an inlet for fluid to be filtered and an outlet for the filtered fluid, and more particularly to a bifurcated inlet for fluids in which turbulence in the bottom of the chamber adjacent the fluid inlet is controlled.
It is known in the art to utilize filters of the pressure type wherein a pressure differential in the liquid being filtered is maintained at opposite sides of a filtering element. Such filters typically use filter elements formed of porous or finely perforated tubes. Uses of such filters are typically for filtering dry cleaning solvents and the like. The operation of such filters is relatively simple. Filtering is usually accomplished by a diatomaceous earth in suspension, with the solvent to be filtered being forced through filter tubes thereby reducing the size of the interstices or perforations in the tube wall and thus enhancing filter operation, such as the removal of lint and dirt from the solvent.
Cleaning of these types of filters is, in concept, quite simple. Generally, the fluid flow is stopped with the result that the diatomaceous earth is allowed to fall to the bottom of the container and settle since it is generally heavier than the solvent. Thereafter, the filtered material may be drained off. Contemporaneously with the cessation of fluid movement is the shaking of the filters known as "bumping". This is generally accomplished by mounting the filter elements on a plate which may be moved while still in the vessel. By moving the plate which holds the filter elements, and striking it abruptly against a barrier or stop, the remaining particles of diatomaceous earth and filtered matter are shaken off the filter elements and hence the use of the word "bumping". Immediately prior to bumping of the filter, backwashing may be accomplished in order to further dislodge matter from the filters. An example of this may be found in U.S. Pat. No. 3,100,190 "Pressure Filter and Filter Tube Therefor" issued Aug. 6, 1963 to R. B. Hobson, Jr. A related disclosure may also be found in U.S. Pat. No. 3,642,141 "Filter Tube and Connection Thereof to Tube Sheet" issued Feb. 15, 1972, to Hobson, Jr. Both of these patents are specifically incorporated by reference herein. These references disclose bump-type filters and are particularly drawn to the filter element therein.
Moreover, these references utilize a fluid inlet wherein the incoming liquid picks the filter medium, such as diatomaceous earth, up off the floor of the container so as to deposit it, or redeposit it, on the filter tube's exterior surfaces in order to perform its filtering function. This is accomplished by use of an elbow on the inlet pipe looking downward toward the the bottom of the container. The fluid stream therefore hits the floor and stirs the accumulated solids into a suspension. In large filters, the flow can be so great that the filter tubes themselves are disturbed by the turbulence (e.g. 2000 gpm in a 60 inch diameter unit). Further, since the bottom ends of the tubes are not anchored in any way, the turbulence can "hammer" the tubes, causing interstitial squirming. The filtering material and/or dirt may also be forced to slide through to the clean side and go downstream into the process thereby defeating the entire purpose of the filter.
Another disadvantage is that there is a tendency for bridging of the diatomaceous earth adjacent the plate where the filter tube is attached thereto. This significantly affects filter performance during operation. Further, the filter must be cleared and hence bumped more frequently and it is more difficult to clean the tubes. Further, in the present system, "Stratification" of the filter media is a problem. This occurs as a result of diatomaceous earth coming from the bottom of the vessel up. Gradually, more earth is deposited at the bottom of the tubes than at the top. This causes a disproportionate deposition of filter media on the tubes with the result that the tubes must be bumped prematurely since the bottom of the tubes will clog up much more quickly than the remaining substantial portion of the tube.